Cold Spray Coatings of Al Alloys for Corrosion Resistance

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1 1 Cold Spray Coatings of Al Alloys for Corrosion Resistance Benjamin Hauch Benjamin Maier, DJ Devan, Kumar Sridharan*, Todd Allen University of Wisconsin - Madison *Contact: kumar@engr.wisc.edu 1

2 Presentation Outline 2 Cold Spray Coating Process Installation + Operation of CGT Kinetiks Cold Spraying of AA5083 powder & AA5083 H116 substrates Future Work 2

3 Cold Spray A Low Temperature Process Low temperature, high velocity Ideally suited for spraying metallic materials E.g. Al & alloys, Cu, stainless steel 3 Leads to corrosion-resistant coatings Little or no oxide inclusions in coating Little or no porosity in coatings Good interfacial bonding (minimal thermal expansion effects) Davis, JR. Handbook of Thermal Spray Technology,p.77,

4 Cold Spray Deposition Model 4 High P, T gas High velocity gas High velocity (2-3 Mach) powder impinges substrate surface Particle temperature kept low : solid state deposition with no melting 4

5 University of Wisconsin Cold Spray System 5 Sound-proof spray booth CGT KINETIKS 4000 Sound-reducing booth 50kg 6-axis robot Sample stage and dust collector Robot for pre-programmed movement of spray gun Propellant gas cylinders Robot (left) and CGT (right) controllers 5

6 Initial System Usage: CP Aluminum Powder 6 Cold Spray Coating (Al) Al 6061 Substrate Al H15 Si 0.0 Fe 0.11 Cu 0.0 Mn 0.0 Mg 0.0 Cr 0.0 Zn 0.0 Ti 0.0 Al Bal. Dense coatings of pure Al deposited on 6061 alloy substrate 6

7 X-Ray Diffraction: CP Al & Cold Spray Coatings 7 (220) (111) (200) (220) (311) Comparison of X-ray spectra indicate no oxide phases are introduced Peak broadening for the cold sprayed coating indicates nonuniform strain due to plastic deformation 7

8 AA 5083 Material Stock 8 4-5Mg Mn H116 temper plate He atomized powder Large <20µm fraction 8

9 Cold Spray Parameter Selection 9 Process Variables Investigated: Gas pre-heat temperature Gas pressure Spray Distance (SD) Constants: Nitrogen carrier gas Powder flow rate Rastering program Gas temperature & pressure convert into high gas / particle velocity 9

10 X-Ray Diffraction of AA 5083 Material and Coating 10 No evidence of contamination via oxidation or β- phase precipitation as a result of the cold spray coating process Unit cell size peak shifts (alloying) and peak broadening (cold spraying) are observed 10

11 Cross-sectional Microscopy of Cold Sprayed C 35 bar 41 mm 400 C 35 bar 41 mm 100 µm Coating dense, but interface delaminations observable Improved interface adhesion 11

12 Cross-sectional Microscopy of Cold Sprayed C 39 bar 26 mm Improved interface adhesion & appearance 12

13 Cross-sectional Microscopy of Cold Sprayed C 39 bar 26 mm 240 µm Coating Substrate Gas temperature increased 50 C Excellent coating, minimal interface defects 13

14 Cross-sectional Microscopy of Cold Sprayed C 39 bar 18 mm Offset distance decreased to 18mm Good increase in observed quality 14

15 Cross-sectional X-Ray Mapping of Cold Sprayed C 39 bar 18 mm EDS measurements cannot distinguish between coating & substrate (above & below blue line) 15

16 Microhardness Evaluation of Cold Sprayed C 39 bar 18 mm Higher hardness of cold spray coating is indicative of good densification and work-hardening 16

17 NAMLT Sample Preparation C 40 bar 26 mm 6 sided Coating Milling (~50 µm removed) Milling performed to remove outermost deposited layer (loosely compacted, not representative of rest of coating) 17

18 Post-Deposition Processing of Cold Spray Coatings: Milling C 39 bar 26 mm 4 passes, ~18 g/min powder feed rate, 1000 mm/s robot speed 8 passes, 9 g/min powder feed rate, 400 mm/s robot speed Deposited coating can be milled in order to produce smooth surface without coating delamination 18

19 Modified NAMLT Testing 19 NAMLT not designed for coatings Inefficient to coat 6 sided samples One-sided test being investigated with Carderock As-rec H-116 Coated 450 C 40 bar 26 mm 19

20 Corrosion Repair: Cold Spray Deposition on Sensitized mg/cm² Mg Al 5083AA coating can be deposited on heavily sensitized 5083AA substrate 20

21 Dimensional Restoration Via Cold Spray: ~3x1 mm gouge H116 Cold-sprayed 5083 powder A simplistic deposition model correctly predicted the geometric features of the resultant coating 21

22 Potentiodynamic Testing of Substrate and Coating Coating: 475 C 40 bar 26 mm AA As-Received Substrate 5083AA Cold Spray Coating (475 o C, 40bar, offset: 26mm) Test Condition: milled surface Test Solution: ASTM Synthetic sea salt (D 1141) (36 g/l NaCl, MgCl 2, Na 2 SO 4, ) 5083AA Substrate 5083AA Coating 22

23 Immediate Future Work 23 Continued optimization of coating parameters Powder size distribution & temperature Continued NAMLT, Modified NAMLT, and electrochemical testing of 5083 coatings & substrate samples Coating Adhesion Tests (ASTM C633) Expand collaborative activities with Naval Surface Warfare Center and other industries He & He/N 2 gas blends for higher velocity deposition & more difficult materials: (shown to produce noticeable higher coatings densities) 23

24 Conclusions 24 UW has successfully deposited AA 5083 onto AA 5083 H116 in as received, sensitized, and damaged surface conditions As-deposited AA 5083 exhibits higher hardness than and similar corrosion properties to bulk AA 5083 H116 Cold spray of metals and oxidation-sensitive materials results in deposition without oxidation or melting Powder = Coating 24

25 Acknolwedgements 25 We gratefully acknowledge the support of ONR Award #: N and DoD-ONR DURIP award for this research 25